1. Field of the Invention
The present invention relates to a lighting unit including two types of light sources, to a backlight unit including such a lighting unit, and to a liquid crystal display device equipped with the backlight unit.
2. Description of the Related Art
A liquid crystal display device is usually configured such that a backlight unit supplies a display light since a display element is non-emissive. As FIG. 7 illustrates, there is a configuration in which an optical member such as a diffusing plate (not shown in FIG. 7) is combined with a lighting unit 100 including a plurality of aligned white light sources 101 such that display light is provided uniformly in an in-plane direction of a display surface of the liquid crystal display device.
Fluorescent lights are usually used as white light sources 101 in the lighting unit 100. The use of fluorescent light has a problem that color purity of display light generated by fluorescent light is low since light purity of R is generally lower than that of G or B in the fluorescent light.
Therefore, in order to improve color reproducibility of an image on a liquid crystal display device, Japanese Unexamined Patent Application Publication No. 2004-139876 discloses a backlight unit shown in FIG. 8, which includes the optical members and a lighting unit 110 including two types of light sources; fluorescent lights 111 and LEDs (Light Emitting Diodes) 112.
In the lighting unit 110, red spectrum characteristics are eliminated from the fluorescent lights 111; therefore, the fluorescent lights 111 having only blue spectrum characteristics and green spectrum characteristics are used. Combinational use of those fluorescent lights 111 with the LEDs 112 having red spectrum characteristics generates high color purity in R, G, and B. As a result, the lighting unit 110 provides high color reproducibility.
Japanese Unexamined Patent Application Publication No. 2003-187623 also discloses a lighting unit including LEDs of plural types for emitting light of different colors.
However, the conventional configuration disclosed in Japanese Unexamined Patent Application Publication No. 2004-139876 experiences a problem described below.
That is, in the lighting unit 110 in Japanese Unexamined Patent Application Publication No. 2004-139876, the two types of light sources must be arranged on an irradiation plane without overlapping each other. Thus, the lighting unit 110 cannot obtain the uniform display light in the both types of light sources.
Take FIG. 8 as an example, when a pitch between neighboring fluorescent lights 111 is 2L, a pitch between the endmost fluorescent light 111 and an end portion of the lighting unit 110 is L. As a result, light outgoing from the fluorescent lights 111 will be uniform. On the other hand, the LEDs 112 are arranged respectively between the fluorescent lights 111. Therefore, when a pitch between the neighboring LEDs 112 is 2L, a pitch between the endmost LED 112 and the end portion of the lighting unit 110 is 2L. As a result, the light intensity of the light outgoing from the LEDs 112 is insufficient at the end portions. Thus, the display light around the end portions of the lighting unit is bluish due to insufficient red light intensity.